clear

isStale

Returns whether the state of this observable is stale and is expected to
change soon. A non-stale observable that becomes stale will notify its
stale listeners. A stale object that becomes non-stale does so by
changing its state and notifying its change listeners, it does not
notify its stale listeners about becoming non-stale. Clients that do not
expect asynchronous changes may ignore staleness of observable objects.